The invention relates to a droplet separator for separating liquid droplets as well as the solid matter and condensate associated therewith from a gas flow brought into rotary motion, which droplet separator comprises a gas flow duct and a droplet separation tube surrounding it, and in which the outermost layer of the gas flow is arranged to be passed from the flow duct into the droplet separation tube for separating the droplets, and the gas flow made free from droplets is arranged to be passed from the droplet separation tube back into the flow duct.
Liquid in droplet form is often present in gas flows, which liquid is desired to be removed. The removal of droplets is necessary particularly when a gas flow is blown out. The liquid droplets flying out of a flow tube contaminate the surroundings depending on the velocity of exhaust either in the immediate surroundings of an exhaust pipe or chimney, or in the case of a high chimney, even at a distance.
Different materials made of porous materials have been used for separating liquid droplets from a gas flow. There are known plugs of suitably close or open structure, made of natural fibres, metal wire or different plastic fibres, which plugs are placed in a flow duct. There are also known metal or plastic sieves placed one upon the other or plate packages made of perforated plates, the aim of which is to cause liquid to be separated from gas onto the surfaces of a droplet separator while the gas flow has to make rapid changes in the direction of flow. The sharper the changes of direction the gas flow must make and the higher the number of the slot or plate openings through which it must flow, the better the liquid droplets will be separated. These known separators suffer from the drawback of being clogged for two reasons. One reason is the dust and solid matter particles possibly present in the gas flow. The other reason is the crystallization phenomenon, which results from the fact that supersaturated liquid drops are formed on the surfaces of the droplet separator, from which drops solid matter causing clogging begins to crystallize onto the openings and/or walls of the droplet separator.
One known problem-solution is the so-called Euroform plate arrangement, in which gas starts a laminar flow after the edge of the plates situated in close overlapping relationship. The surface of flow is provided with an elongated pocket extending transversely to the direction of flow, into which pocket the liquid or liquid drop present in the gas flow falls because of its specific gravity. Since this groove is further at an oblique angle with respect to the gas flow, the liquid separated from it is guided along the groove to one end thereof, from which it is guided to an outlet, and the gas free from droplets continues its flow. The drawback of this arrangement is also that the grooves are filled up because of the solid matter which is contained in the gas or which crystallizes from the liquid. This means that the gas flows through the entire plate package without the droplets being separated because the grooves intended to separate the droplets have clogged up.
In most cases, static droplet separators do not function satisfactorily at least in conditions in which there is a risk of clogging or of the grooves being filled because of the solid matter content of the gas flow or if the liquid droplets in question have a tendency to form supersaturated and crystallizing concentrations in separated droplets.
Consequently, there is a need to find other solutions for the separation of droplets. One such solution is a cyclone separator. It operates fairly well if the gas flow contains enough droplets, which are washing the inner surface of the cyclone all the time preventing solid matter from sticking to the inner walls of the cyclone. The drawback of the cyclone separator is, however, limited droplet sizes. Mists and vapours smaller than a given separation threshold, which mists and vapours can be separated by means of the above-mentioned fibre bed filters, pass through the cyclone separator. The other drawbacks of the cyclone separator include its large size and the need to place the cyclone in an upright position.
An object of the invention is to reduce the problems associated with the known droplet separators.
A further object of the invention is to provide a droplet separator which operates without trouble not only in the conditions described above but also in conditions in which a high exhaust chimney may cause a liquid to be condensed from supersaturated gas. This kind of situation is often encountered, for example, in high uninsulated chimneys of wet washers particularly in winter, when the cold walls of the chimney cause condensation of the liquid contained in the gas flow. If there is no droplet separator at the end of the chimney, droplets and condensed liquid visibly flow along the outer wall of the chimney forming dirty streaks, and condensate droplets also often fly to the surroundings of the chimney.
The droplet separator according to the invention is characterized in that a gas flow duct is formed of three successive parts placed at a distance from one another in the direction of flow, which parts are a flow tube, a cone part tapering in the direction of flow, and a continuation tube, the diameter of the front end of said cone part being smaller than the diameter of the flow tube and the rear end thereof being at a suitable distance from the continuation tube, whereby flow gaps are formed between said successive parts of the flow duct, which gaps provide an open flow connection between the flow duct and a droplet separation tube.
The droplet separator according to the invention is suitable for separation of liquid from gas which flows in a horizontal, oblique or vertical tube, in which connection the droplet separator may be situated in the middle of the flow tube or at its end. The gas and the additional liquid possibly fed into it are brought into a rotating flow motion before the droplet separator in order to produce a centrifugal field in the gas flow such that the droplets and liquid heavier than the gas are caused to flow with the gas along the inner wall of the flow tube. The main part of the gas flow entering the droplet separator enters the tapering cone part, the front end of which is smaller in diameter than the flow tube of gas and which is situated at a small distance from the end of said flow tube, whereby a gap is formed between the end of the flow tube and the front end of the cone part. Through said gap, part of the gas containing liquid and flowing along the outer wall of the flow tube can flow as a thin ring into an expansion part which is situated outside the cone part and in which the liquid and droplets are separated from the gas flow. If the flow tube is in an upright position, the separated liquid returns from an annular collecting space situated outside the flow tube through openings provided in the walls of the flow tube back into the tube in which it flows down along the inner surface of the flow tube. If the flow tube is inclined or in a horizontal position, the tube is provided with a separate opening through which the liquid is passed out.